Hi guys,
I just discoverd this "site/forum" to my great delight...well I wasn't living in the jungle all these years!

Well,I am planning on building an acoustic guitar preamp incorporating
1; a Piezo under saddle pu,an AST type ex;B-Band AST1470
or a schertler bluestik under saddle pu.
a Panaonic WM 61A elecret condenser mic (found some on the e-bay) I've a few more to experiment with....

For the tone control..thought of using the TDA 1524A IC since it has stereo in/out!

I 've been looking at some published designs,so would like to combine some of them.

My problem is, although I can read,& construct from schematics
have no knowledge of circuit theory or analysis!

Part1:Piezo Preamp(tone control)
I' lifted this schematic from http://www.next.gr & have already tried this on a proto-board & it worked the first time!
But since I wanted to drive it on +/- 9v supply for better dynamic response,(wishful thinking?) I then removed resistor R12.
It sounded little clearer than when it was run on only + 9v. although still lacking a wee bit in bass.But it sounds rather lifeless,(only 10dB gain)but sounds much better than most piezo preamps I've heard so far!

By the way I'm using a Roland AC60 for testing this.

Also tried as a current follower by increasing R1 from 1M to 4M7 & shunting it to ground, with higher values of C1 but it still sounded very harsh & typical piezo!So have now reverted back to as before.

GAIN SWITCH:
No sound on either 0dB or-10dB settings!Quite adequate sound only on +10dB setting

Question
Would it be possible/better to run the input/buffer as a comparator instead?
Is it possible get +40dB gain in this configuaration?
What component changes/additions would it involve?
How do I calculate the queisent current?

Can any one out there please give me any suggestions/ideas?
All inputs/ideas are gratefully taken onboard.

This is the bugger I was ranting about!Thanks a million...I was actually trying to forward it with my query..but for some strange reason it just didn't come up!but then you beat me to it.Well done & thanks again.

Hello Mark,
Thanks for the Carwin schematic,which I've just had a look at...
as you will agree, this too is only a 2 stage + tone control design apart from the FET in the input buffer section + seperate active/ passive pickup drive circuits.

I am using a 20mm ceramic disc..as described in the original article.& it sounds quite good too!

I have tested " mine" on a Roland AC 60 ac.amp & IT DOES WORK! albeit with rather reduced bass & gain response.However,
it feedsback with all the tone controls turned up full & the AC 60 turned up half +!It also sounds much better so unlike most piezo preamps I've tried,including the Artec Tri-Blender on one of my guitars!

My AC60 has a 1M impedence in the dedicated piezo input,may be
this is too low for an under saddle/Piezo film pu's..but works well with this ceramic disc.

If you have a look at the resistor R1 which sets the impedence,I'd agree that this is quite low compared to the feed-back resistors..hence the low gain?

Hi Lineup,
Could you please explain the effect og high gain vs. dynamic range?Am I correct in supposing that increasing th voltage gain would give more dynamic range aswell due o more headroom avilable to the signal?

Is this the reason that studio mixers/ high spec;mic channel preamps have this "large sound"?
I've tried about 20 odd acoustic guitar preampsso far..yet almost all of them sound the same,regardless with either a cermic or a undersaddle pickup!This may not be very critical on solid electric bass,since i presume,the vibrations come mainly from the bridge area & not from the body? But on hollow string intruments,the whole body vibrates,hence more resonance frequencies?
Besides the piezo generates only a very small amount current! ,
which cannot provide adequate signal boost to the input/buffer opamp?

I also gather that API & the Presonus AcouticQ preamps have 60dB & 40dB gain respectively!

1.How can I achieve more gain without loosing higher freq.
2.would it help to run it on +15/-15v instead?
3.could I cascade more stage(s) to achieve this?.